Air pollution and cognitive function in older adults

As a resident of Los Angeles, one of the most polluted cities in the United States, I think a lot about the air we breathe. It’s well established that outdoor air pollution is a health threat — exposure to high pollution concentrations has been linked to increased risk of respiratory and cardiovascular damage, emergency room visits and hospitalization, and premature mortality. What I find particularly alarming is the mounting evidence demonstrating links between urban air pollution and damage to the structures and functioning of the brain.

Most of the research on pollution and the brain has been conducted in animals, and human research is largely focused on brain development in children. In a study published in The Journals of Gerontology, Series B: Social Sciences, a colleague and I sought to determine if exposure to air pollution has consequences for the aging brain as well.

Although several air pollutants are harmful to human health, I’m especially concerned about particulate matter air pollution, a byproduct of industrial activities and automobile emissions. Fine particulate matter, or PM 2.5, includes particles that are 2.5µm (microns) in diameter and smaller. To put this in perspective, a grain of fine beach sand is around 90µm in diameter. Due to their small size, fine particles can be inhaled deep into the lungs and may even deposit in the brain by traversing the thin lining of epithelial cells separating the nasal cavity from the brain.

To determine if PM 2.5 is important to the aging brain, we examined differences in cognitive function between older adults living in low and high pollution environments. Information on annual PM 2.5 concentrations at the census tract level was linked to data on participants ages 55 and older in the Americans’ Changing Lives (ACL) study. Cognitive function was assessed with an abbreviated form of the Short Portable Mental Status Questionnaire (SPMSQ), which consists of a subtraction test of working memory and recall of the date and names of the president and vice president to assess orientation.

Study participants lived in areas with an average PM2.5 concentration of 13.8μg/m3 (micrograms per cubic meter). The National Ambient Air Quality Standard (NAAQS) for fine particles, which is determined by the Environmental Protection Agency (EPA) to be the level at which there is increased risk to human health, is 12.0μg/m3. Nearly two-thirds of the study participants lived in areas where annual PM2.5 concentrations exceed the NAAQS.

We found that a 10 unit increase in PM 2.5 was associated with a 1.5 times greater error rate on the cognitive assessment, suggesting older adults living in high pollution areas have worse cognitive function compared to those living in low pollution environments. Importantly, this difference was not explained by individual demographic, social, and economic factors, length of time at residence, or neighborhood socioeconomic composition.

The negative health impacts of air pollution present a challenge, considering how much of our activities involve going outdoors and being around traffic emissions, if not industrial emissions. As individuals, we can become more aware of our local air quality. Just as we check the weather forecast when planning our day, we should also check the daily air quality index. AirNow.gov compiles data from the EPA’s air monitoring networks to provide information on local air quality in real time. Each day the Air Quality Index (AQI) provides a value indicating how clean or polluted the local outdoor air is. Values are coded to reflect underlying health concerns and range from ‘good’ to ‘hazardous’ to one’s health. Days when AQI levels are considered to be unhealthy may not be the best days to undertake major physical exertion outdoors, especially for sensitive populations, such as older adults with a history of respiratory or cardiovascular problems.

The good news is that air quality has improved in the United States in recent decades. Since the EPA introduced the first air quality standards for PM 2.5 in the late 1990s, national annual concentrations of PM 2.5 have decreased 34%. With the new standards released in 2012, we can expect to see further reductions in air pollution.

The population of older adults living in large metropolitan is growing rapidly as a result of population aging. This study highlights a possible modifiable risk factor for cognitive decline in older adults. If we can reduce our exposure to air pollution, through individual or national efforts, we’ll all breathe a little easier.